Every motor is different.
Combustion chamber shape, head material, piston dome configuration, squish height/quench clearance, static CR, cam specs, installed ICL, spark plug heat range. Ignition timing, ambient air temperature, intake charge temperature, coolant temperature. Manitold pressure,, exhaust valve temperature. Piston crown temperature, fuel air ratio.

It ALL MATTERS, and ements affect a motor's octane requirements.

If you know your actual mathematical static CR, your quench clearance (if it's more than .060" then your octane requirements will be higher), your cam specs, and your (warm) cranking compression, then you can make a pretty good guess.

I like this spreadsheet...good info.

Hate to hijack this post but saw that mild thunder runs B&M 420 tried to message but Private Message full sir.

Mr. Thunder
saw your post on B&M 420 blower i have same thing in Apache i am purchasing only set at 3-4 lbs now and rev limiter set a 5400 plan on updating to MSD box raise to 5800 and like to run 6-8 lbs boost is your motor similar.

mine
588 ci
420 blower
chiller
8:1 compression
merlin heads.
93 octane

tks
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Maybe for a non intercooled old school Roots blower..

I ran 10 PSI with my Procharged 555 cid 8.6:1 compression.. worked just FINE without "race gas"

I couldn't see the HP or TQ, what'd it make? (Sorry, didn't see the big "1020" up there. What TQ)

PS---"Lago Vista? Is that Grandbury behind you? or did you go to Dynatek at Lake Lavon? Who has a dyno at Grandbury?

Lake Travis

Dyno belongs to my buddy Bob, who used to run Full Throttle Marine in Spicewood

Don't know that this is our "best" run.. But gives you an idea.. Boat ran STRONG.. But I've now moved on to twin "stock" engines..

Thanks for the sheet BI. I'm going to run 10psi on my set up, not near the cubic inches, but it sure gives me motivation to get it done!!!